There are very few objective criteria for the choice between conservative and surgical treatment of lumbar and dorsolumbar scoliosis ranging from 40 to 50 degrees. We reviewed the long-term results obtained in 76 patients treated with plaster braces because they had refused surgical treatment; in 56% of the cases a nearly 10 degree gain was maintained after the onset of treatment; all of the cases which showed improvement presented a reduction in the curve by at least half and rotation by at least one-third in tests in suspension or in bending, and this was maintained in plaster. In cases where the long-term results were poor, however, rotation did not change. In conclusion, of the many parameters examined, only a combined assessment of the reducibility of both the Cobb angle and of rotation provides a valid indication for the treatment of lumbar and dorsolumbar curves ranging from 40 to 50 degrees.